PSA whitening toothpastes are just normal toothpastes with added abrasives. So they temporary whiten your teeth because you’ve removed the outer most enamel which gives your teeth its hardness. At the mere cost of tooth sensitivity and future staining, the deeper dentine layer is much softer and porous which is easily damaged by acidic foods but also more easily stained due to the porosity. So congratulations your teeth are now more stained.